Pilot-scale Preparation And Separation Of Lignin-based Sunscreen Microcapsules

With the destruction of the ozone layer,ultraviolet radiations becoming increasingly severe,which will cause skin disease such as sunburn and accelerated aging,affecting human health.Therefore,sun protection and skin care are urgent.In plants,the content of lignin is second only to cellulose,and it is the most abundant aromatic polymer biomass in nature.The natural aromatic skeleton and macromolecular structure endow lignin with good ultraviolet absorption and light stability.The phenolic hydroxyl group in the lgnin molecule can scavenge free radicals and endow lignin with excellent antioxidant properties.Also,lignin has good biocompatibility and is an ideal choice for preparing green sunscreens.However,due to the small conjugated structure and disordered aggregation of lignin,the absorption of long-wave ultraviolet(UVA)is insufficient,and the absorption potential of medium-wave ultraviolet(UVB)is remained to developed.Therefore,it is necessary to synergize lignin with chemical sunscreen agents to prepare microcapsules.In this paper,on the basis of the preliminary small-scale experiment,the pilot-scale preparation and separation process research of microcapsules is carried out to provide theoretical guidance and technical support for the engineering application.Firstly,using enzymatic hydrolyzed lignin(EHL)as the wall material,chemical sunscreen octyl methoxycinnamate(OMC)and avobenzone(BMDM)as the core materials,the lignin-based sunscreen microcapsules were self-assemblyprepared by ultrasonic shear dispersion and cavitation.The total amount of raw materials in the pilot test is 10 kg,which is1000 times larger than small-sacle experiment with total amount of 0.01 kg.Optimum preparation conditions are optimized as: water-oil mass ratio is 7:3,power = 1900 W,surfactant addition amount is 15 wt%,ultrasonic time is 90 min.The initial particle size of the prepared microcapsules was 123 nm,and the particle size only increased by 34 nm after 30 days.The loading amount of the chemical sunscreen agent in the microcapsule is 60.4%.The natural three-dimensional network structure of EHL in the capsule wall and the cross-linking effect in the ultrasonic process make the microcapsules have good storage stability and can effectively prevent the leakage of chemical sunscreen agents.The(OMC+BMDM)/EHL microcapsules prepared in the pilot test can maintain good sun protection performance.Adding 10 wt% microcapsules to formulate a sunscreen with a whiteness of 32 and a sun protection factor(SPF)value of 134,which maintained at 103 after 12 hours of ultraviolet radiation,showing good light stability.Further,in view of the problems of low processing volume and cumbersome process for removing unreacted lignin by centrifugal separation of small-scale experimental products,ceramic membranes were selected to separate and purify the microcapsule products with large processing volume and high separation efficiency.According to the particle size of lignin sunscreen microcapsules,a ceramic membrane with a pore size of 50 nm was selected for the separation study.The membrane flux of the microcapsule dispersion was initially 0.435 L/h and dropped to 0 at 3 h.Than water was added to replace the incompletely removed lignin.The total amount of water was 1.5L and the lignin was removed after separation for 2 h.The initial particle size of the microcapsule product is 112 nm,and it remains at 118 nm after separation,showing a spherical structure.The vitro sun protection performance analysis showed that the separated and purified microcapsule products have better sun protection performance due to the improved purity,and the SPF value of sunscreen(with lignin microcapsules content of 10 wt%)is increased to 153.Compared with the small-scale centrifugal separation,the pilot-scale ceramic membrane separation process has a better separation efficiency(processing capacity/separation time)increased by 2.5 times,and simpler operation process,which has important guiding significance to promote the engineering application of lignin sunscreen microcapsule products.